In general, as synthetic fibers for artificial hair for the decoration of hair on the head, such as wigs and hair pieces, acrylic synthetic fibers or vinyl chloride synthetic fibers are frequently used.
Conventionally, as fibers for artificial hair having bulkiness and soft texture, fibers having a Y-shaped cross section in which three projections extend from a central connecting part in three directions and a portion near the top of each projection becomes narrow have been proposed (see Patent Document 1). Moreover, as fibers for artificial hair which are naturally shiny and have soft texture, fibers having a cross section in which three or more projections radially extend from one central connecting part and groove-like irregularities parallel to the direction of the fiber axis are provided have been proposed (see Patent Document 2). However, these fibers have room for improvement as fibers for artificial hair in terms of processability, such as smoothness of combing and ease of braiding hair into three strands. Moreover, as fibers for artificial hair excellent in processability at the time of crimping or braiding hair into three strands, fibers which have a flat cross section and which are bent or curved at an angle exceeding 90° at one portion or two portions have been proposed (see Patent Document 3). However, in the case of such flat fibers, bulkiness has been insufficient.
Conventionally, fibers having modified flat cross sections with various shapes are known. For example, Japanese Unexamined Patent Publication No. 60-162868 relates to an electrically-conductive polyester filament, and describes fibers having a trunk and two projections extending in opposite directions with the trunk interposed therebetween as fibers on which a metal coating is hard to form uniformly and easily (see Comparative Example 1 and FIG. 3E of Cited Reference 4). However, Japanese Unexamined Patent Publication No. 60-162868 describes that this polyester filament is used for producing an electrically conductive filament by chemical plating, but does not describe that the polyester filament is applied to artificial hair. Japanese Unexamined Patent Publication No. 61-89321 describes a highly dyeable polyester fiber which is flat and has two projections at each of the outer peripheral parts across the major axis (see FIG. 1 of Cited Reference 5 and, for the shape of a nozzle outlet, FIG. 4 thereof). However, Japanese Unexamined Patent Publication No. 61-89321 describes a fiber which has a single yarn fineness of 0.5 to 8 deniers (about 0.6 to 8.9 dtex) and is formed into yarn to be used for woven and knitted articles (see the left upper column, lines 8 to 14 on page 4 of Cited Reference 5), but does not describe that the fiber is applied to artificial hair. Moreover, the fiber is excessively thin as artificial hair, and is difficult to process. Furthermore, Japanese Unexamined Patent Publication No. 3-51349 describes a fiber having a modified cross section which has an oval shape with an ellipticity of 1.2 to 2.5 and in which two projections crossing the major axis at a flat part and extending from each of both sides of the major axis are provided at intervals (see Patent Document 6). However, Japanese Unexamined Patent Publication No. 3-51349 describes a polyester fiber forming a pile part of a napped pile fabric for car seats, but does not describe that the fiber is applied to artificial hair. Moreover, the single yarn denier of the polyester fiber is 0.7 to 4.0 (about 0.8 to 4.4 dtex) (see the lower right column, lines 18 to 19 on page 2 of Patent Document 6). Since the size of the fiber is excessively thin, the fiber is not suitable for an artificial hair application. Furthermore, Japanese Unexamined Patent Publication No. 6-81207 describes a fiber having a specific cross section in which two projections crossing the major axis at a flat part and extending from each of both sides of the major axis are provided at intervals (see claim 1 and FIG. 1 of Cited Reference 7). However, Japanese Unexamined Patent Publication No. 6-81207 describes that the fiber having a specific cross section is used for panty hose as covering yarn, but does not describe that the fiber is applied to artificial hair. Moreover, the single yarn denier of the specific cross section is 1.0 to 5.0 (about 1.2 to 5.5 dtex). Since the size of the fiber is excessively thin, the fiber is not suitable for an artificial hair application.
Patent Document 1: Japanese Unexamined Patent Publication No. 8-296112
Patent Document 2: Japanese Unexamined Patent Publication No. 8-296115
Patent Document 3: Japanese Unexamined Patent Publication No. 9-132813
Patent Document 4: Japanese Unexamined Patent Publication No. 60-162868
Patent Document 5: Japanese Unexamined Patent Publication No. 61-89321
Patent Document 6: Japanese Unexamined Patent Publication No. 3-51349
Patent Document 7: Japanese Unexamined Patent Publication No. 6-81207